From the Inbox: Navel Orange Fruit Drop

From a Correspondent:

I have a navel orange tree that flowered like crazy, produced a ton of fruit but 99% of the fruit fell off. I have one orange as of now and the same thing happened to my dad's tree as well. Do you know why that is happening? He has lemons and limes that are doing great.
Karri,
Henderson, Nevada

Good morning Karri,
Isn't that annoying? Flowers everywhere, and then suddenly all seems for naught.

All citrus trees experience a certain amount of fruit-drop, but Navel Oranges in particular "shed unusually freely," which is the academic way of saying: hey, all the fruit fell off! Citrus fruit drop is often called "June drop" because it happens in May.

May and June are typically the most stressful season for plants in the Desert Garden. The Spring rains are past, the temperatures are rising markedly, and the atmospheric humidity of the monsoon season is still in the future. In response to these stressors, citrus trees "balance the load" by dropping excess fruit. It's essentially a physiological response to conditions that helps to ensure that the tree has no more fruit than it can support.

Remember, with all fruits, while our goal is food, the tree's "goal" is reproduction. So from a tree's perspective, if it had one, which it doesn't, because it's a plant, but let's not quibble, a very few healthy fruits (with their seeds) is a better situation than tons of struggling fruit. That gives us a clue as to why Navel Oranges are more prone to "shed unusually freely."

Navel Oranges are mutant sports of another orange tree, and they don't produce fruit sexually; they produce fruit parthenocarpically, meaning without cross-fertilization. The term itself is from the Greek, parthenos meaning virgin, and carpos meaning fruit. And that fruit is seedless, so, while from our perspective a Navel Orange tree may be productively loaded with wonderful fruit, technically the tree is sterile.

Bear with me, I am going somewhere with this.

When June drop occurs and a citrus tree begins to shed excess fruit, priority is given to fertilized fruit. You noted that your dad's lemons and limes are doing fine; I would bet a donut that they also lost fruit, but since most of their fruit is fertilized, they kept much more on the tree than did the Navel. The Navel fruit is sterile, so of lower priority in the grand scheme of reproduction.

What do you do about it? The key is to remember that it's the stressors that trigger June drop, so the solution for future years is to minimize the effects of the stressors. As the weather heats up and dries up in late Spring, be certain that your Navel tree has been watered deeply and is thoroughly hydrated. We tend to not worry about upping the irrigation until full Summer, but it's late Spring that nails the tree. You can't go by the calendar. This year, for instance, the Desert Garden stayed pretty cool fairly late, and then heated up fast in early May. Each year is different.

As always, the goal is deep but infrequent irrigation. Try to get the root zone, out to the canopy of the tree, watered to depth of three feet into the ground. This gives the tree moisture reserves to draw on, and encourages deep rooting. Don't let the tree stand in wet soil, though; this can also be a stressor.

Along with your deep irrigation, be careful about how you fertilize your tree. Always give the first dose of fertilizer at or before full bloom, water it in thoroughly, and use lower amounts than listed on the fertilizer label. Three small doses of fertilizer spread over time is a much better method than one big dose all at once. I recommend not fertilizing again until the fruits are at least the size of a golf ball and June drop is past. We typically over-fertilize our home citrus, so err on the side of restraint.

And now for the good news: little green citrus fruit are adept at hiding among the leaves until sometime much later in the year when they suddenly turn bright orange and surprise you. You may still have more fruit this year than you think.

I hope this helps,
Tyler

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A Little Earth Day Television

For something a little different on Earth Day, I spent part of the morning down at the ABC 15 studios talking about vegetable gardening on the Sonoran Living morning show. You can view the segment by clicking on the video link to the right, on this page. It went pretty well, due entirely to the host, Stephanie Sandoval; one of the things that always interests me about seeing the "inside" is the realization of how much skill it takes to make things look easy.
Tyler

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From the Inbox: Tomato Pruning and Soil

From a correspondent:

I have a question about soil and compost: Can I use potting soil and regular dirt, mixed, instead of compost? If not, can I purchase compost? Also with tomato plants when they start to bear fruit, should I wean out leaves and bottom shoots ? I have three plants that I started with, and they are starting to bloom and bear fruit.
Bob, Casa Grande, Arizona

Good morning Bob,
Great questions, and both issues are important in the Desert Garden.

First to the soil and compost. Whenever possible, the foundation for your vegetable garden should be your native soil. Real soil, the kind we buy with the house, is chock full of desirable minerals and other plant nutrients; the minerals we eat in our vegetables come from the soil in which they grew. Potting soil doesn't have those good qualities.

So our goal always is to amend out native soil with compost or other organic material, rather than to use potting soil (besides, by volume, potting soil is expensive!) And don't be tempted to mix potting soil in as a substitute for compost; it really isn't the same thing and it won't do a good job. If you're not yet making your own compost, you can buy it in bags or in bulk. Mix it onto your native garden soil, and you're on your way.

Now for the tomatoes: make life easier on yourself and on your tomatoes, and don't pinch out leaves and bottom shoots. In other climates, gardeners often pinch out extra tomato shoots and leaves to open up the plant, promoting ripening and light in the interior. Here in the Desert Garden, we want to do just the opposite.

Very soon now, our weather will be steadily hot and sunny, and that's hard on the tomatoes. If you leave the leaves and shoots, they help to form a shady and cooler canopy that will help to protect the ripening fruit; that's one of the best ways to ensure good tomatoes in the desert.

I hope this helps,
Tyler

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From the Inbox: Plant in basins, not hills

A correspondent recently wrote in to ask why all the seed packets for melons and squash tell us to plant the seeds in mounds, or hills.

Simple answer: Because the people who write the seed packets don't live in the desert.

For much of the country, excess water can be one of the downfalls of the vegetable garden. Soggy soil results in seeds that rot before they sprout, cold soil with no air, and rotting roots in already growing plants. Their solution – and it's a good one – is to plant on raised ridges, hills, or mounds that allow the soil to warm and drain.

Excess rainfall is not a problem in the Desert Garden, and following the seed-packet advice can cause your plants to fail. There's two reasons:

First, we want our garden planting areas to collect as much rain water as they can, and to hold as much irrigation water as possible; anything that leads water away from your vegetables can result in dry soils and consequent poor plant growth.

The second, and less intuitive, reason has to do with our salty soils and water. If you've ever watered a patch of bare desert soil and then let it dry out in the sun, you may have noticed a white or yellowish-white residue left on the soil surface; if there are clods of dirt in the area, they may have been completely encased in this residue. That residue is made up of salts that have been dissolved out of the soil and have then migrated to the soil surface. As the water evaporates out of the soil, the salts are deposited at the highest point of evaporation. If we were to plant our vegetables on ridges or mounds, the highest point of evaporation would be right where the seedlings come out of the soil, resulting in salt deposition at the tender spot where the roots meet the stem at soil level; if you recall what the Romans did to Carthage, you know that's really bad for our plants.

So here's what we do instead: after you've prepared your soil by digging in plenty of compost, use a rake, or your hands, to form a planting basin. Just pull some soil aside to make little "walls" that surround the area you'll be planting, then plant your seeds or plants in the bottom of that basin. Not only will that allow rain and irrigation water to collect where it's most needed, but it will also result in the salts being deposited on the high edges of the basin, well away from the plants.

I hope this helps,

Tyler

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From the Inbox: Spacing Corn

Joanne in Henderson, Nevada, left a comment the other day, in which she mentioned she might be planting corn in two 2-foot by 8-foot by 12-inch-high raised beds.

Corn is one of the vegetables for which spacing makes all the difference. You can scatter tomatoes all around the yard, plant peppers in amongst your roses, and sow your carrots willy-nilly, but not so with corn. Corn is unique in being the only grain we grow with any regularity in the home garden and, as with all grain, corn is wind-pollinated; this has practical consequences.

Corn pollen is produced in a tassel at the very top of the plant; these tassels are the "male" parts of the plant. The "female" parts of the plant are the ears formed in the leaf axils along the stalks. From each of these ears extends a cluster of what we call "silk." The far, unseen end of each silk thread is attached to a corn-kernel-in-waiting down inside the ear on what will eventually be the corn cob. What this means is that in order for a grain of corn to form, pollen must travel from the top of the plant, to deep inside the ear, all without any help – and this has to happen for every single kernel of corn.

On a perfectly calm and still day, it is possible that pollen might fall straight down from the tassels, land on the silks, and form a kernel. On a day like today, when the wind is blowing like mad, and rose petals are scampering back and forth across my yard like a flock of frightened sheep, there is a good chance that all the pollen will simply blow away – and that is the number one cause of failure when growing home corn.

The way we get around that is to always plant corn in blocks rather than in long rows. That way, the blowing pollen will likely blow onto the silks on the next plant over and pollinate the kernels.

All of which might be a long-winded way of suggesting, Joanne, that you want to be certain your corn isn't' stretched out in two 8-foot rows, but is rather in more of a block. If your beds are adjacent along the 8-foot sides, consider planting 2 four-foot rows at one end (the same end) of each, for a total of 16 plants, and then using the remaining end of each bed for either a different crop or a later planting of corn.

I hope this helps,
Tyler

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New Vegetable and Composting Classes

I'll be putting together a new series of vegetable gardening and composting classes in the next few weeks. The classes are always small, to ensure plenty of hands-on instruction, so space is limited. If you're interested in getting information about the classes when the schedule is finished, send me an e-mail to get on the list. As always, put "Desert Garden" in the subject line, and be sure to let me know if you're more interested in weekday or Saturday classes.
Tyler

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From the Inbox: Potted lemon

From a Correspondent:

I have a potted dwarf Lisbon Lemon that is 3 years old. It finally has bloomed just recently but just doesn't seem joyous. Some of the leaves have a yellowing vein pattern. I imagine it is a deficiency or that I need to repot. Where would you recommend to go for deficiency diagnosis? I want to make my tree as happy as can be! Haven't had much luck with some of the nurseries or blogs.
Thank a bunch,
Isabella
Tempe, Arizona

Good morning Isabella,
Don't spend your time or money on any kind of testing for soil deficiency. Growing citrus in pots in the Desert Garden does take a little extra care, but not that much. As your lemon is three years old and blooming, you've done a good job so far, and only a couple of adjustments are needed if you want it to really thrive.

First, in looking at the picture you sent, it appears that the yellowing leaves are primarily older leaves, from last year or the year before. As with all evergreen plants, the plant as a whole says green year-round, but the individual leaves have a finite life-span. This time of year, it's perfectly normal to see the older leaves on a citrus tree fade, turn yellow, and fall. I'm guessing that's what you're seeing, so there's no cause for concern on that account.

But, let's take a broader look at citrus in pots.

When they grow in the ground, trees have several natural advantages: they have (in theory) unlimited space in which to spread their roots; they have a natural reserve of moisture in the soil; their roots are kept cool by the lower temperatures underground; and the trees can tap into the naturally occurring soil minerals. These are all essential for the tree's health and growth, and they are all missing in a potted tree. Our job, when we grow a tree in a pot, is to keep these lacking elements in mind, and to compensate for them as much as possible.

If you take a look at the picture you sent me, you'll notice that it's a big tree in a little pot; you're right: it's time to re-pot. Your tree needs additional root space to maintain a moisture reserve and cooler roots.

Think about a typical 105° Summer day in the Desert Garden; even if the pot is not in direct Sun, over the course of the day the pot and the soil in it will heat up, just by virtue of the surrounding air temperature. The larger the pot, the slower the soil heating , and the larger the moisture reserve.

You're not going to want to re-pot a lemon tree every few years, so I recommend getting a large pot, some good soil-based potting soil, and re-potting now. Do your tree a favor and get a pot with straight sides. Tapered pots like the one you have now are not very good for trees in the long run; they have a small soil volume compared to their top diameter, and they also have a tendency to tip over once the tree gets larger. Be certain your new pot has a drainage hole and – here's the exciting part – do not use gravel, sand, old potsherds, or anything else to "improve" the drainage at the bottom. Contrary to popular wisdom, gravel in the bottom of a pot will impede drainage, not improve it.

And, last, because your lemon tree will not have much in the way of minerals from its artificial soil, you'll want to fertilize it several times a year with a citrus fertilizer. I recommend using the fertilizer at a rate of about one-quarter the rate recommended on the fertilizer label. Your potted lemon will respond better to several very small and well-spaced doses of fertilizer, rather than one big one, and too much at one time will stress the plant and possibly damage it. Whenever we fertilize, either in a pot or in the ground, always water first, then scratch in the fertilizer, then water again; this should prevent the fertilizer from "burning" the roots. These light fertilizer applications will take care of any mineral deficiencies that are showing up in the leaves.

I hope this helps,
Tyler

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